Mobile excavating machines are commonplace in commercial industries. These machines often have hydraulically-driven rotator assemblies for rotation of manipulating or grappling equipment secured to the end of the articulated booms. These rotator assemblies have oil pressure lines that must be displaced with the rotator assembly, as the grappling equipment is swivelled. These rotator assemblies also are capable of continuous rotation about their main shaft. However, a disadvantage of some of these rotator assemblies is that they have heavy mechanical parts.
With most prior art rotator assemblies, because the grappling equipment is connected directly to the rotator assembly, the rotor assembly parts are subjected to torque and different axial or radial loads. These loads induce stress on the collector and lead to wearing of bearings, seals and couplings. The collector eventually also can develop hydraulic fluid leaks, thereby necessitating repairs. In certain cases, replacement of the entire rotator assembly and grappling equipment is required, which increases maintenance costs.
US 2004/0168568 describes an example of a rotator found in prior art. In such a rotator design, the lower end of the load-bearing shaft is provided with annular oil distribution channels which are in communication with oil pressure line connectors, which extend through the collector jacket. These oil distribution channels communicate with supply channels which are bored into the load-bearing shaft, and oil is fed to the supply channels through oil line connectors, which connect to the oil pressure lines. However, this design is still relatively bulky in size.
U.S. Pat. No. 6,266,901 discloses another example of a rotator found in the prior art. In this case, the oil supply channels are placed in proximity of each other in symmetrical configurations within the rotator structure. Unfortunately, this design also results in a relatively bulky design which causes stresses to the rotator structure due to the rotative movement of the internal components such as the oil supply channels which have an offset with respect to the center axis of the rotator.
Thus, there is still presently a need for an improved rotator design that is small in size and incurs lower maintenance costs due to improved rotative movement of its internal components.
Additionally, there is a need for an improved hydraulic valve design. If an operator wishes to immobilise an object being held with the grappling equipment, the operator must control valves that feed the rotator hydraulic line. The rotator hydraulic line is thus theoretically isolated from the other hydraulic lines. In certain cases, the rotator axis might be immobilised in a horizontal configuration. In this configuration, the load might not be aligned with the rotator axis and consequently, the motor must act to maintain the load in place. However, internal leaks in the hydraulic system result in that a small quantity of oil is sent to the rotator hydraulic line. In this situation, the hydraulic pressure increases on both sides of the motor. This condition is problematic for the motor. It is much more efficient to maintain a load in place if the low pressure side of the motor is drained towards the hydraulic reservoir. A pressure relief valve is therefore required to decrease pressure on the low-pressure side of the motor.
Prior art relief valves include hot oil shuttle valves. In these types of valves, the flow paths are connected or isolated by means of a movable sliding member. However, these valves are susceptible to internal oil leaks which decrease the capacity of the motor to maintain a load in place.
Consequently, there is still presently a need for a new type of hydraulic valve, which can decrease this pressure surrounding the motor when the rotator is immobilising an object being manipulated.